In a typical communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and/or user equipments (UE), communicate via a Radio Access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, with each service area or cell area being served by a radio network node such as a radio access node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be denoted, for example, a “NodeB” or “eNodeB”. A service area or cell area is a geographical area where radio coverage is provided by the radio network node. The radio network node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio network node.
A Universal Mobile Telecommunications System (UMTS) is a third generation (3G) telecommunication network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several radio network nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural radio network nodes connected thereto. This type of connection is sometimes referred to as a backhaul connection. The RNCs and BSCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio network nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of an RNC are distributed between the radio network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio network nodes, this interface being denoted the X2 interface. EPS is the Evolved 3GPP Packet Switched Domain. FIG. 1 is an overview of the EPC architecture. This architecture is defined in 3GPP TS 23.401 v.13.4.0 wherein a definition of a Packet Data Network Gateway (P-GW), a Serving Gateway (S-GW), a Policy and Charging Rules Function (PCRF), a Mobility Management Entity (MME) and a wireless or mobile device (UE) is found. The LTE radio access, E-UTRAN, comprises one or more eNBs. FIG. 2 shows the overall E-UTRAN architecture and is further defined in for example 3GPP TS 36.300 v.13.1.0. The E-UTRAN comprises eNBs, providing a user plane comprising the protocol layers Packet Data Convergence Protocol (PDCP)/Radio Link Control (RLC)/Medium Access Control (MAC)/Physical layer (PHY), and a control plane comprising Radio Resource Control (RRC) protocol in addition to the user plane protocols towards the wireless device. The radio network nodes are interconnected with each other by means of the X2 interface. The radio network nodes are also connected by means of the S1 interface to the EPC, more specifically to the MME by means of an S1-MME interface and to the S-GW by means of an S1-U interface.
The S1-MME interface is used for control plane between eNodeB/E-UTRAN and MME. The main protocols used in this interface are S1 Application Protocol (S1-AP) and Stream Control Transmission Protocol (SCTP). S1AP is the application layer protocol between the radio network node and the MME and SCTP for example guarantees delivery of signaling messages between MME and the radio network node. The transport network layer is based on Internet Protocol (IP).
Establishment of the S1-MME interface on S1AP protocol level is shown in FIG. 3 as the S1 setup procedure. The purpose of the S1 Setup procedure is to exchange application level data needed for the radio network node and the MME to correctly interoperate on the S1 interface. The radio network node may initiate the procedure by sending an S1 SETUP REQUEST message to the MME once it has gained IP connectivity and it has been configured with at least one Tracking Area Indicator (TAI). The TAI(s) are used by the radio network node to locate IP-addresses of the different MMEs, possibly in different MME pools. The radio network node includes its global radio network node identity and other information in the S1 SETUP REQUEST message. The MME responds with an S1 SETUP RESPONSE message. This S1 SETUP RESPONSE message includes for example the Globally Unique MME identifier(s) (GUMMEI) of the MME.
An Initial Context Setup process is shown in FIG. 4. An INITIAL CONTEXT SETUP REQUEST message is sent by the MME to request the setup of a wireless device context or context of a wireless device. This INITIAL CONTEXT SETUP REQUEST message comprises information related to both the wireless device context and different E-RABs to be established. For each E-RAB the MME includes E-RAB Quality of Service (QoS) parameters such as QoS Class Identifier (QCI) and Allocation and Retention Priority (ARP). The QCI is a scalar that is used as a reference to radio access node-specific parameters that control bearer level packet forwarding treatment, e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc., and that have been pre-configured by the operator owning the radio network node. An INITIAL CONTEXT SETUP RESPONSE message is sent by eNB to the MME confirming the setup. Current assumption is that the RAN-CN split is similar for 5G as for 4G, implying an (evolved) S1 interface.
In LTE a Discontinuous Reception (DRX) cycle is used to enable the wireless device to save its battery. The DRX cycle is used in Radio Resource Control (RRC) idle mode but it can also be used in RRC connected mode. Examples of DRX cycles or lengths of DRX cycles currently used in RRC idle mode are 320 ms, 640 ms, 1.28 s and 2.56 s. Examples of lengths of DRX cycles currently used in RRC connected mode may range from 2 ms to 2.56 s.
The DRX cycle is configured by a network node such as a radio network node or a core network node and the DRX cycle consists of an “on period” part and a “sleep period”. During the “on period”, the wireless device monitors a set of the DL channels. The set of DL channels depends on the RRC mode in which the wireless device is i.e. Connected Mode or Idle Mode. In these “on periods”, the wireless device also performs measurements, e.g. intra/inter frequencies, inter-Radio Access Technology (RAT), etc, by e.g. in LTE monitoring the Primary Synchronization Signal (PSS)/Secondary Synchronization Signal (SSS) and Cell specific Reference signals (C-RS). This on period is denoted as On duration. During the on duration of the DRX cycle, a timer called ‘onDurationTimer’, which is configured by the network node, is running. This timer specifies a number of consecutive control channel subframes, e.g. Physical Downlink Control Channel (PDCCH), enhanced Physical Downlink Control Channel (ePDCCH) subframe(s), at the beginning of a DRX Cycle. It is also interchangeably called as DRX ON period. More specifically it is the duration in downlink subframes that the wireless device after waking up from DRX to receive control channel, e.g. PDCCH or ePDCCH. If the wireless device successfully decodes the control channel, e.g. PDCCH or ePDCCH, during the ON duration then the wireless device starts a drx-inactivity timer and stays awake until its expiry. When the onDurationTimer is running the wireless device is considered to be in a DRX mode of the DRX cycle.
The drx-inactivity timer specifies the number of consecutive control channel, e.g. PDCCH or ePDCCH, subframe(s) after the subframe in which a control channel, e.g. PDCCH, indicates an initial UL or DL user data transmission for this Medium Access Control (MAC) entity. It is also configured by the network node. When the drx-inactivity timer is running the wireless device is considered to be in a non-DRX mode i.e. no DRX is used. An active time is the time the duration during which the wireless device monitors the control channel, e.g. PDCCH or ePDCCH. In other words this is the total duration during which the wireless device is awake. This includes the “on-duration” of the DRX cycle, the time during which the wireless device is performing continuous reception while the drx-inactivity timer has not expired and the time the wireless device is performing continuous reception while waiting for a DL retransmission after one Hybrid Automatic Repeat Request Round-Trip Time (HARQ RTT). The minimum active time is equal to the length of an on duration, and the maximum active time is undefined (infinite). Thus, if the wireless device receives a DL message during the “on” duration, the wireless device exits its DRX cycle, starts a “DRX inactivity timer”, and continuously monitors the corresponding DL channels until the timer expires.
During the “sleep period”, the wireless device is not mandated to monitor the DL channels and, therefore, the wireless device cannot be reached for DL transmissions during this time.
The DRX ON and DRX OFF durations of the DRX cycle are shown in FIG. 5. The DRX operation with more detailed parameters in LTE is illustrated in FIG. 6.
Hence, in LTE, DRX functionality can be configured for both RRC_IDLE and RRC_CONNECTED wireless devices. The wireless device restarts the DRX Inactivity Timer each time the wireless device gets DL data and, when the timer expires the wireless device starts its DRX cycle again. In Connected Mode, the wireless device starts a short DRX cycle, if configured. Otherwise, the wireless device starts a long DRX cycle. If the wireless device does not receive any DL message during the “DRX short cycle timer” period, the wireless device enters the second, long, DRX cycle.
In Idle Mode, there is only one DRX cycle. The DRX cycle is also known as “Paging Cycle”. When using DRX in RRC_IDLE mode in LTE, during the “on period”, the wireless device monitors the DL for paging messages intended for the wireless device. The paging cycles and paging occasion which are applicable for a wireless device may be configured in system information or may be provided via dedicated signaling by the network. In LTE, paging is triggered by the core network (CN), and the paging cycles correspond to the core network configuration.
In 3G each CN domain can have its own paging cycle either wireless device specific or default. In order to make the wireless device only wake up once to receive paging from Circuit Switched (CS) CN or from Packet Switched (PS) CN or from both the paging cycles are multiple of each others and Paging Occasion (PO) is based on International Mobile Subscriber Identity (IMSI) of the wireless device in both cases.
In LTE Idle Mode, the paging cycles configure the paging frames and occasions when a wireless device may expect a paging indication. This also means that the wireless device may sleep at other times.
The paging frames may be calculated using the following formula from 3GPP TS 36.304 v12.4.0:SFN mod T=(T div N)*(UE_ID mod N)
Where T is the assigned DRX_cycle, and DRX_cycle is the DRX cycle, or paging cycle, configured for the Wireless device in Idle Mode. And UE_ID is the IMSI of the wireless device. The wireless device monitors the same occasions also in connected mode but only for system information update notifications.N=min(T,nB), nB={4T,2T,T,T/2,T/4 . . . }
DRX cycle=Paging cycle
Within the paging frame, there is a concrete paging occasion, subframe (i_s), which the wireless device monitors.i_s=floor(UE_ID/N) mod Ns 
DRX parameters of System Information (SI) stored in the wireless device shall be updated locally in the wireless device whenever the DRX parameter values are changed in the SI. If the wireless device has no IMSI, for instance when making an emergency call without Universal Subscriber Identity Module (USIM), the wireless device shall use as default identity UE_ID=0 in the Paging Frames (PF) and i_s formulas above.
The following Parameters are used for the calculation of the PF and i_s:                T: DRX cycle of the wireless device. T is determined by the shortest of the wireless device specific DRX value, if allocated by upper layers, and a default DRX value broadcast in system information. If wireless device specific DRX is not configured by upper layers, the default value is applied.        nB: 4T, 2T, T, T/2, T/4, T/8, T/16, T/32.        N: min(T,nB)        Ns: max(1,nB/T)        UE_ID: IMSI mod 1024.        
IMSI is given as sequence of digits of type Integer (0 . . . 9), IMSI shall in the formulae above be interpreted as a decimal integer number, where the first digit given in the sequence represents the highest order digit.
For example:IMSI=12(digit1=1,digit2=2)
In the calculations, this shall be interpreted as the decimal integer “12”, not 30 “1×16+2=18”.
Ns: max(1,nB/T)
nB is a parameter which is directly mapped the number of resources the network wants to allocate for paging purposes. For example, if the configured DRX cycle is 64 radio frames and nB is set to T or lower, the network may only send paging indications once every 64 radio frames. Therefore, all the wireless devices will wake up at the same SFN. If the nB is set to 2T, the network may send paging indications at two different times within the 64 radio frames.
There may be several paging frames within a DRX cycle. In each of the paging frames, there may be one or more paging occasions, one or more sub-frames within a paging frame. Wireless devices are grouped and distributed among the resources dedicated for paging.
A system frame is equivalent in LTE to 10 ms.
There may be cases in which the radio network node may not be able to locate the wireless device. This could happen, for example, in error cases when the wireless device moves to Idle Mode autonomously. In this case, the radio network node may not be aware that the wireless device has moved to this mode and the wireless device may not be monitoring any longer the paging occasions configured by the radio network node, and the wireless device may be following the CN paging cycles. Another case is when RAN's paging area is smaller than the wireless device's mobility area, the area which the wireless device can move within without updating the network. This may result in that the radio network node may not be able to locate the wireless device by a radio network node paging procedure reducing or limiting the performance of the communication network.